Were the new subfolders in IMAP or saved on your computer in a POP account or under "Local Folders"? If they were only on the IMAP server, they might not have been on your computer at all. If those folders were saved on your computer, then the files will be under your Thunderbird Profile folder, under the "Mail" folder. Go to this link to learn about [[Profiles - Where Thunderbird stores your messages and other user data]] Quit Thunderbird. First backup your entire Thunderbird Profile folder to another location for safekeeping. In the "Mail" folder is a folder for "Local Folders", and folders for each POP e-mail account you have set up. Keep going down through the folders until you find the Thunderbird folder names you are looking for. For each one of the Thunderbird folders, you will see two files. One without a file extension, and one with the file extension .MSF. You will also probably see a Windows folder with the name+.mozmsgs. For one of the folders that you are missing, delete the file with the .MSF extension. That file doesn't contain the e-mails, just information that Thunderbird uses to keep track of the e-mails. Then run Thunderbird and see if that particular folder shows up. If it does, then quit Thunderbird again, then go and delete the .MSF files for the other "missing" Thunderbird e-mail folders. To show all file extensions, if you don't see them: Windows 7: Windows Explorer: -Click the "Tools" menu on the menu bar. Click the "Folder Options" item in the popup menu that appears. - A dialog box appears. Click the "View" tab at the top of the window. - Look for a setting "Hide file extensions for known file types" and uncheck the box beside it to disable it. - Click "OK"